U.S. banks speculate that foreign nations, organized crime or terrorists are behind efforts to cripple their websites and warn that costs to keep intruders at bay will rise. President Barack Obama directed the government on February 12th to develop voluntary cyber security standards for companies running vital infrastructure and plans to push Congress to set formal rules.

'We are going to see more disclosures, and that’s a warning sign that things are really getting bad', said Lawrence Ponemon, chairman of Ponemon Institute LLC, a Traverse City, Michigan-based security research firm, which predicts a 30% increase in expenses tied to cyber intrusions this year.

Attacks in December hit Bank of America Corp. (BAC), JPMorgan Chase & Co. (JPM), U.S. Bancorp, Wells Fargo & Co. (WFC) and SunTrust Banks Inc. (STI), two executives at security companies said at the time. PNC Financial Services Group Inc., the second-biggest regional bank, said in its annual filing that cyber attacks may hurt customer confidence and increase costs at the Pittsburgh-based company.